This invention relates to an electron microscope, and in particular to a scanning electron microscope which is suitable for use in observation, inspection, or measurement of semiconductors.
Scanning electron microscopes have long been used to inspect or observe semiconductor devices. Among such scanning electron microscopes, there are electron beam testers in which electrons obtained from the sample are energy-discriminated, an electric potential contrast image is created based on discriminated electrons, and inspections are performed for defects in the wiring of semiconductor devices. Japanese Patent Laid-open No. 10-313027 discloses an electron beam tester and a method of wiring defect inspection using this electron beam tester.
The above patent publication discloses a technique for judging whether a specific site of the sample is electrically isolated, by static electrification of the sample and confirmation of the extent of static charge in the electrified region.
If a specific member (such as wiring) on the sample is electrically isolated from other members, as a result of the above static electrification, electric charge accumulates in this specific member. On the other hand, if the specific member is electrically grounded, there is no accumulation of static charge. By observing this static charge state, it is possible to judge, for example, whether wiring has been broken.
The above reference discloses a method in which, by intentionally applying static charge to the sample surface, and using a charged particle beam device comprising an energy filter to observe electric potential contrasts, breaks and defects in electric wiring or similar formed on the sample surface are inspected. However, there is the following problem.
In general, by applying a certain negative voltage to a mesh-shape electrode, the energy filter used in a scanning electron microscope selectively detects electrons having a higher acceleration voltage than the applied voltage. However, a mesh-shape electrode is physically large, and so among the secondary electrons or reflected electrons which are generated or reflected by the sample, there are electrons which collide with this mesh-shape electrode. Although these electrons carry information about the sample, they are lost without being detected.
The present invention is intended to resolve this problem, and has as an object the effective utilization of secondary electrons and/or reflected electrons which collide with a mesh-shape electrode and are lost in a scanning electron microscope comprising an energy filter.
In order to achieve the above object, the present invention provides a scanning electron microscope comprising an electron source, a focusing lens which focuses a primary electron beam emitted from the electron source, a porous electrode to form an electric field which performs energy filtering of electrons obtained as a result of irradiation of the above sample by the above primary electron beam, focused by the focusing lens, and a first electron detector which detects electrons passing through the porous electrode; characterized in further comprising a porous structure positioned closer to the above sample than the above porous electrode, a deflector positioned closer to the above sample than to the porous structure and which deflects electrons away from the axis of the above primary electron beam, and a second electron detector which detects electrons deflected by the deflector.
Secondary electrons and reflected electrons which collide with the porous structure generate secondary electrons as a result of the collision. In this invention, by using a second electron detector to detect the secondary electrons, it becomes possible to use in inspections and measurements the electrons which collide with the energy filter, and which previously could not be detected.
This invention makes possible various observations, inspections and measurements which heretofore could not be performed, based on the secondary electrons detected by this second electron detector.